refactor: IpUtil 코드 구조화 개선

- 매직넘버 상수화
- 메서드 책임별 분리

Author: toothlessdev

src/main/java/life/mosu/mosuserver/global/util/IpUtil.java

@@ -1,48 +1,62 @@
 package life.mosu.mosuserver.global.util;
 
 import jakarta.servlet.http.HttpServletRequest;
-import java.net.InetAddress;
-import java.net.UnknownHostException;
+import java.util.List;
+import java.util.Arrays;
+import java.util.stream.Stream;
+
+import lombok.Getter;
+import lombok.RequiredArgsConstructor;
 import lombok.experimental.UtilityClass;
 
 @UtilityClass
 public class IpUtil {
 
-    public static String getClientIp(HttpServletRequest request) throws UnknownHostException {
-        String ip = request.getHeader("X-Forwarded-For");
+    private static final List<String> IP_HEADERS = Arrays.asList(
+            "X-Forwarded-For",
+            "Proxy-Client-IP",
+            "WL-Proxy-Client-IP",
+            "HTTP_CLIENT_IP",
+            "HTTP_X_FORWARDED_FOR",
+            "X-Real-IP"
+    );
+
+    public static String getClientIp(HttpServletRequest request) {
+        String ip = IP_HEADERS.stream()
+                .map(request::getHeader)
+                .filter(IpUtil::isValidIp)
+                .findFirst()
+                .orElse(request.getRemoteAddr());
+
+        String proxiedIp = resolveProxiedIp(ip);
+        return Loopback.resolve(proxiedIp);
+    }
 
+    private static String resolveProxiedIp(String ip) {
         if (ip != null && ip.contains(",")) {
-            ip = ip.split(",")[0].trim();
+            return ip.split(",")[0].trim();
         }
+        return ip;
+    }
 
-        if (isInvalidIp(ip)) {
-            ip = request.getHeader("Proxy-Client-IP");
-        }
-        if (isInvalidIp(ip)) {
-            ip = request.getHeader("WL-Proxy-Client-IP");
-        }
-        if (isInvalidIp(ip)) {
-            ip = request.getHeader("HTTP_CLIENT_IP");
-        }
-        if (isInvalidIp(ip)) {
-            ip = request.getHeader("HTTP_X_FORWARDED_FOR");
-        }
-        if (isInvalidIp(ip)) {
-            ip = request.getHeader("X-Real-IP");
-        }
-        if (isInvalidIp(ip)) {
-            ip = request.getRemoteAddr();
-        }
+    private static boolean isValidIp(String ip) {
+        return ip != null && !ip.isEmpty() && !"unknown".equalsIgnoreCase(ip);
+    }
 
-        if ("127.0.0.1".equals(ip) || "0:0:0:0:0:0:0:1".equals(ip)) {
-            InetAddress inetAddress = InetAddress.getLocalHost();
-            ip = inetAddress.getHostName() + "/" + inetAddress.getHostAddress();
-        }
+    @RequiredArgsConstructor
+    @Getter
+    private enum Loopback {
+        V4("127.0.0.1"),
+        V6("0:0:0:0:0:0:0:1");
 
-        return ip;
-    }
+        private final String address;
 
-    private static boolean isInvalidIp(String ip) {
-        return ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip);
+        public static boolean isLoopback(String ip) {
+            return Arrays.stream(Loopback.values())
+                    .anyMatch(loopback -> loopback.getAddress().equals(ip));
+        }
+        public static String resolve(String ip) {
+            return isLoopback(ip) ? "localhost" : ip;
+        }
     }
 }